Many movable barrier operators monitor applied force (typically by monitoring a parameter that varies as a function of force) as corresponds to movement of a movable barrier and use such information to determine when the movable barrier has encountered an obstacle (such as a person or item of personal property). Upon sensing such an obstacle, the operator will typically initiate a predetermined action such as reversing the movement of the barrier. In particular, the operator usually compares present applied force against a threshold that represents excessive force to identify such an occurrence.
Unfortunately, a factory-set static excessive force threshold will typically not provide satisfactory results under all operating conditions and/or for all installations. The reasons are numerous and varied. The physical dimensions of a given installation can vary dramatically (both with respect to barrier travel distance and barrier weight as well as other manifest conditions) and these physical conditions can and will in turn impact the amount of force required to move the barrier. The physical interface between the barrier and its corresponding track or pathway can also vary, sometimes considerably, over the length of barrier travel. Such variations can each, in turn, be attended by significantly varying force requirements. Temperature, too, can have a significant impact on necessary force, as temperature (and especially colder temperatures) can alter the physical relationships noted above and can also significantly impact upon at least the initial operating characteristics of a motor as is used to move the barrier. Force needs, measurements, and/or behaviors can also vary with respect to time, as the physical conditions themselves change, as the motor ages, and even with respect to how long a motor has been recently operating.
To attempt to accommodate such circumstances, many movable barrier operators have a user-adjustment interface (usually one or two potentiometer-style knobs) that a user or installer can manipulate to adjust allowed applied force during one or more directions of barrier travel. Unfortunately, even when used correctly, force settings established in this way can become outdated. Another solution has been to provide a learning mode during which a movable barrier operator can monitor force conditions during movement of the barrier and use such information to automatically establish an excess-force threshold to be used during subsequent normal operations. Unfortunately, again, force setting values established in this way can become outdated (and sometimes within a short period of time).
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.